Your old ads had a historical CTR / performance component that helped position your listings. Once you deleted and removed you started over from scratch and you are given a dummy CTR for awhile until you prove yourself. That is my understanding at least.
That's probably it. Your position is based on your CPC and your CTR. Right now, your positions are probably soley based on your CPC. Some marketers will bid very aggressively on their CPCs for the first several days of a new campaign in order to rank high and try to establish establish a good CTR. Then, lower their CPC and let that high CTR carry them for a while. If you still get clicks, you're good to go.